root用户执行 适用于有外网权限的机器
配置一个外网的yum源， 安装了telnet vim net-tools 命令
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
curl -o /etc/yum.repos.d/epel.repo https://mirrors.aliyun.com/repo/epel-7.reposudo
yum clean all
yum makecache
yum install -y telnet vim net-tools